1. Field of the Invention
The present invention relates to an actuator using a piezo-electric element and particularly relates to an actuator in which a large force is obtained at a large displacement point.
2. Discussion of the Related Art
In a control board or the like using a programmable controller, in many cases, an input signal from an operation switch is not required to be continuous but may be a pulse signal. For such a use, an element for generating a pulse signal in response to an operation may be used as a switch in place of a conventional push-button switch or the like having a mechanical contact.
Additionally, it is known that a piezo-electric element generates an electric charge when an external force is applied thereto. If this phenomenon is utilized, the pulse signal can be generated without supplying any external electric power.
In order to obtain a pulse signal by utilizing a piezo-electric element, it is necessary to apply instantaneous strain to the piezo-electric element. When a piezo-electric actuator consists solely of a piezo-electric element, it is necessary to separately provide a mechanism for converting a gradually-changing switch operation force into a impact force. As a result, the whole configuration becomes complicated and expensive.
Further, fluid pressure (oil pressure, air pressure, etc.), or an electromagnet is widely used as a drive source for an actuator for applying an operating force to various equipment. Recently, however, an actuator utilizing deflection generated when a voltage is applied to an piezo-electric element, such as piezo-electric ceramics or the like (hereinafter, referred to as a piezo-electric actuator), has been developed. The piezo-electric actuator has various advantages, such as increasing response speed, generating no noise, and reducing the required size and load.
Generally, the generation force of an actuator using fluid pressure is constant independently of the displacement of an operating end portion. The generation force of an actuator using an electromagnet, on the other hand, becomes maximum at the maximum displacement point because the maximum displacement point is the same as the point where the needle is attracted by the stator.
In a piezo-electric actuator, however, there has been a problem in that, since the generation force in the piezo-electric element during deflection becomes smaller as the quantity of displacement thereof becomes larger, a large force cannot be obtained at a large displacement point. Conventionally, therefore, a mechanism for enlarging a load has been separately provided because it is difficult to independently use the piezo-electric actuator.